Without limiting the scope of the invention, its background is described in connection with historical sources of cells of hematopoietic lineage for cell therapy. Cell therapy is utilized for the treatment of a number of diseases including inborn errors and acquired malignancies. The classical source for cell therapy has been bone marrow although there has been some use of umbilical stem cells and peripheral stem cells isolated by apheresis, which are increasingly being used in lieu of bone marrow.
Mesenchymal stromal (a.k.a. stem) cells (MSC) and hematopoietic stem cells (HSCs) have been identified as two main sources of adult stem cells. MSCs have been described as tissue resident adult multipotent cells that develop from embryonic mesodermal germ layer. MSCs have a high capacity of self-renewal while maintaining their multipotent differentiation potential. MSCs are known to develop into cells of mesodermal origin such as adipocytes, osteocytes, chondrocytes, hepatocytes, and myocytes. See Prockop D J. “Marrow stromal cells as stem cells for nonhematopoietic tissues” Science 276 (1997) 71-74. MSCs have been isolated and characterized from a variety of tissues including bone marrow, adipose tissue, and muscle. Zuk P A, Zhu M, Mizuno H, et al. “Multilineage cells from human adipose tissue: implications for cell-based therapies” Tissue Eng. 7 (2001) 211-228. It has been confirmed that MSCs derived from bone marrow and adipose tissue can be induced into non-mesenchymal neurogenic differentiation as well. Long X, et al. “Neural cell differentiation in vitro from adult human bone marrow mesenchymal stem cells” Stem Cells Dev. 14 (2005) 65-69.
HSCs also originate from the embryonic mesodermal germ layer and they are committed to form blood cell types including myeloid (monocytes and macrophages, neutrophils, erythrocytes, dendritic cells etc.), and lymphoid lineages (T-cells, B-cells, NK-cells). In addition to HSCs, several studies have demonstrated the hematopoietic differentiation potential of embryonic stem cells (ES) in vitro. See Moore K J, et al. “In vitro-differentiated embryonic stem cell macrophages: a model system for studying atherosclerosis-associated macrophage functions” Arterioscler Thromb Vasc Biol. 18 (1998) 1647-1654. It has been shown that ES derived macrophages display specific cell surface markers such as CD 14, CD4, CCR5, CXCR4, and HLA-DR. See Anderson J S, et al. “Derivation of normal macrophages from human embryonic stem (hES) cells for applications in HIV gene therapy” Retrovirology 3 (2006) 24.
Malignant transformation of hematopoietic cells is the common cause of diseases such as leukemia and myeloma. Treatment options for these malignant diseases are limited to chemotherapy, radiation therapy, and bone marrow or cord blood transplant. Each treatment strategy has its own limitations because none provide 100% elimination of transformed cells. Autologous bone marrow or stem cell transplants can be used to treat cancers in remission, however, frequent relapse of malignancies are reported following autologous transplantation of bone marrow since there is a relatively high chance that transformed cells persist in the bone marrow and are retransplanted from the bone marrow collection. Given that both MSCs and HSCs home to the bone marrow in post-embryonic life, it is believed that the bone marrow acts as a reservoir for occult transformed cells and that the malignant transformation is present already in stromal progenitors that escape the selection process typically applied to differentiate between malignant and non-malignant cells.
Due to the considerable risk that transformed or premalignant cells will be reintroduced via the autologous graft, methods of “purging” the graft population of transformed cells have been employed. These purging methods have included negative selection of CD34+ (a cell fraction enriched for HSC), negative selection of tumoral CD20+ cells, chemotherapy in vivo and other toxic treatments. Such procedures are expensive, difficult, not sufficiently effective, delay introduction of the graft, and may damage the cells to be engrafted. See Crippa F, et al. “Infectious complications after autologous CD34-selected peripheral blood stem cell transplantation” Biol Blood Marrow Transplant 8 (2002) 281-289. Subjecting the graft population to agents such as soluble FasL that are intended to selectively kill malignant cells has been suggested as an alternative. See US Patent Publication Serial No. 2008/0241109. Unfortunately, in each of these methods, complete elimination of malignant CD34+ cells is not possible. The cancer stem cell population in hematopoietic cancers such as leukemia is believed to be CD34+. See Bonnet, D. and Dick, J. E. “Human acute myeloid leukemia is organized as a hierarchy that originates from a primitive hematopoietic cell” Nature Medicine 3 (1997) 730.
Use of stem cells collected from the peripheral blood by apheresis also carries a possible or even likely risk of reintroduction of malignant cells because the collection procedure typically involves a mobilization of stem cells from the bone marrow by administration of growth factors such as GM-CSF and G-CSF prior to harvest. See e.g. Osiris U.S. Pat. No. 6,261,549 entitled “Human mesenchymal stem cells from peripheral blood.” A typical process for autologous stem cell transplant includes four phases: an induction phase wherein conventional doses of chemotherapeutic agents are used to reduce the load of malignant cells; a mobilization/harvesting phase wherein growth factors are administered to the patient to induce the proliferation and mobilization of stem cells from the bone marrow into the bloodstream from which the cells are harvested by apheresis; a conditioning phase wherein total body irradiation or other high-potency treatment is administered to the patient to wipe out malignant cells and condition the patient to accept the transplant; and a final engraftment phase wherein stem cells are given back to the patient to reconstitute the immune system. Engraftment takes approximately two to four weeks to begin to be apparent enabling the patient to leave the confines of the hospital.
Recently, autologous HSC transplantation (HSCT) has been applied to the treatment of a large number of different autoimmune diseases including neurologic disorders such as multiple sclerosis, rheumatological disorders such as systemic sclerosis, rheumatoid arthritis, and systemic lupus, immunocytopenias such as immune thrombocytopenia, and inflammatory bowel disease, among others. In one large HSCT study for treatment of severe autoimmunity, stem cells were obtained from bone marrow in a minority of patients while in a majority, stem cells were obtained from the peripheral blood after mobilization with granulocyte colony-stimulating factor (G-CSF) or granulocyte-macrophage colony stimulating factor (GM-CSF). It is noted that mobilization has been associated with disease flares or lethal complications. Gratwohl A et al. “Autologous hematopoietic stem cell transplantation for autoimmune diseases” Bone Marrow Transplantation 35 (2005) 869-879.
Allogenic bone marrow stem cell transplantation is still the most commonly used procedure used to treat hematologic malignancies despite the likelihood of graft-versus-hostdisease (GVHD). In an allogeneic transplant, an HLA compatible donor's bone marrow cells are used to restore bone marrow after high dose chemo and radiation therapy. The disadvantage of an allogenic bone marrow stem cell transplant is the risk of GVHD, which affects the skin, liver and other organs and requires therapy with immunosuppressive drugs. While useful in the treatment of a number of other diseases, including aplastic anemia and other bone marrow failure states, amyloidosis, severe combined immunodeficiency and certain other inborn errors including thalassemia major, sickle cell disease and Wiskott-Aldrich syndrome, allogeneic transplants typically require ablative chemotherapy prior to transplantation.
What is needed is a source of cells that have the hematopoietic regenerative potential of bone marrows cells without the risk of contamination with occult transformed cells residing in the bone marrow compartment. Methods of generating such cells in sufficient in quantity and quality for clinical use have been problematic and there continues be an unmet need for this technology.